Generally speaking, the excessive discharge of a battery of an internal combustion engine drive vehicle such as an automobile often causes the impossibility of starting resulting from the lack of the electricity remaining in the battery and hence the lack of the power for starting an engine starter. A reason why such an accident occurs is that a driver drives the vehicle for a long time without exchanging the battery, but a stronger reason is that a driver uses a room air-conditioner and lights in the vehicle during stopping because of a traffic jam at night which is one of recent traffic problems.
A conventional method for resolving such a problem is to use a spare battery by manual operation, but there is a problem in the method that it is necessary to charge the battery supplementarily by manual operation according to circumstance as a matter of course.
Thus the purpose of the present invention is to supply people with an electric source control device of an internal combustion engine drive vehicle provided with a primary battery and a secondary battery kept in a state in which they are always charged to make it unnecessary to change the battery manually when it is almost discharged.